This invention relates generally to electrical circuit breakers and more particulary to aircraft circuit breakers having a pushbutton actuator provided with a manual opening resistant feature.
Aircraft circuit breakers having a pushbutton actuator for closing a set of electrical contacts in a circuit path are well known. By way of example a circuit breaker of this type is shown and described in coassigned U.S. Pat. No. 3,361,882, the subject matter of which is incorporated herein by this reference. Typically, the pushbutton of such circuit breakers when in the dosed or actuated position can be manually grasped and pulled outwardly to open the contacts and de-actuate the circuit breaker.
Although this feature has served as a convenient mechanism for opening a circuit path, it also provides an easily accessible means for undesirable tampering with the circuit breaker.
An object of the Invention is the provision of a manually resettable circuit breaker which can be manually moved from the closed circuit position to the open circuit position only with the use of a special purpose tool. Another object is the provision of a tamper resistant circuit breaker to prevent undesirable manual opening of the circuit breaker electrical contacts. Yet another object is the provision of a circuit breaker which overcomes the above-noted limitations of the prior art
Briefly, in accordance with the invention, a circuit breaker having a manual reset button is configured so that in the operating, dosed contacts position, there is no exposed surface area for grasping to thereby effectively prevent unauthorized personnel or the like from opening the circuit breaker by pulling out the pushbutton. The circuit breaker is provided with a selected opening to provide access for insertion of a special purpose opening tool to engage a reaction surface and apply a contacts opening force. According to a first embodiment, a pair of diametrically opposed generally L-shaped slots are formed in the pushbutton, the slots having a first portion extending in a direction generally parallel to the longitudinal axis of the pushbutton from the top surface thereof and a second portion extending in a common circumferential direction with the surface of the second portion closest to the top surface of the button forming a reaction surface. A special purpose tool used to mechanically trip the circuit breaker is provided with parallelly extending prongs each having a laterally extending foot extending in opposite directions from one another. The prongs and feet are sized to be receivable in respective first portions of the slots and twistable to insert the feet into the respective second portions of the slots and into alignment with the reaction surface. A force can then be applied to the tool to pull out the pushbutton and manually open the circuit breaker.
The second embodiment is useful with circuit breakers of the type having a plunger capable of motion relative to the pushbutton and attached to the movable contact assembly and which, when the contacts are in the closed position, selected downward movement of the plunger will release the latch maintaining the contacts in the closed position and allow the pushbutton return spring to move the pushbutton upwardly and the contacts opening spring to move the contacts to the open position. In the second embodiment the top face or outer end surface of the pushbutton is provided with a small aperture aligned with a reaction surface on the plunger of the circuit breaker. A special purpose opening tool having an elongated probe portion receivable through the aperture can be used to open the contacts of the circuit breaker by inserting the probe portion through the aperture in the pushbutton end surface and applying sufficient downward force on the plunger.